How do you achieve a retro 3D style, today?
This is a brilliant question. One of the main things was that back then, everything was in grayspace. There was very little in the way of raytracing, so non-lamped areas, reflected (or absorbed) a particularly dead gray. This is apparent even in the most well produced 3D animation and art of the time.
Because processing power was so low, edges weren't beveled, so they were infinitely sharp--a real reality breaker.
Textures were often applied directly to primitive faces so the scale and vanishing points rarely matched between different textures if applied to planes. This gives a kind of &quot;collage&quot; effect that is, besides the gray cast, a hallmark of 90s 3D art.
Also, lighting was really cold, and because of the gray-ness of the surrounding bodies, everything had a gray cast.
I hope this addresses some of the issues in play, though not all of them, I'm sure.